Your revolver should be fired double-action if you are acting in defense. It is a double-action revolver: it's meant to be fired this way.
There are a couple schools of thought on that issue, John.
Given the time, distance, opportunity...and assuming that the imminent threat criteria have been met...I'll absolutely cock the hammer on a double-action revolver in a life nor death situation. Since the purpose of shooting is hitting...and a fast, accurate hit provides the best chance of stopping the fight in time to get me home alive...anything that I can do to expedite that is exactly what I'll do.
Bear with me.
I'm not a cop, and I have no duty to arrest. Nor do I have a duty to challenge or "warn" a violent individual of my armed status or of my intent to shoot. There are several instances of a private citizen issuing a "Freeze! Drop your weapon" challenge and getting shot for it.
I'm not gonna be that guy.
If the situation has degraded to the point that I feel it necessary to draw the gun, the opportunity for conversation has passed, and shooting is pretty much a foregone conclusion. There are certain exceptions, of course. For instance...inside my home or on my property and I've already got him on screen with a shotgun...but it would be advisable to immediately show hands and move slowly.
As for the intent of the double-action revolver...
I do believe that the idea was to cock the gun for that first all-important shot with the DA mode in reserve if a fast followup shot became necessary. At least, that's the way the old-timers saw it.
Of course, if an attack comes so suddenly that the cretin is on top of me as I claw my way to the gun, I'll use the trigger-cocking mode.
As Cooper noted: (paraphrased)
"At powder burning distances, one does not need to be a virtuoso."